The most abundant wavelengths found in sunlight and many artificial bright light sources are those in the green-yellow portion of the spectrum, i.e., 520 nm to 575 nm. In modern poultry houses, artificial illumination may be the only source of light provided to birds; thus, the duration, intensity, and quality of light become important environmental factors, as light influences both reproductive and productive systems in domestic fowl. Light quality can be defined by two criteria: 1) dose intensity, and 2) quality spectra (Andrews and Zimmerman, 1990). In birds from subtropical and temperate latitudes, photostimulation increases egg production, whereas a reduction in photoperiod delays or decreases production. In addition, light intensity plays an important role in rearing birds, mainly because birds need a certain light intensity to be photostimulated (North and Bell, 1990).
The avian eye, similarly to the human eye, is capable of seeing in a narrow part of the light spectrum (up to 760 nm). Apart from the eyes, birds are equipped with active extra-retinal photoreceptors, located in several parts of the brain, which are involved in transduction of photostimulation. As photostimulation of birds is an integral component of sexual maturation and reproductive performance, there have been numerous reports on the effect of different sources (wavelengths) of light on sexual maturation and reproductive performance in birds (see, for instance, Harrison et al., 1970; Scott and Payne, 1937; Ringoen, 1942; Benoit, 1964; and Phogat et al., 1985). For example, in studies using filtered light, increased growth of turkeys was observed when turkeys were exposed to shorter wavelengths (Proudfoot et al., 1979; Gill and Leighton, 1984; Levenick and Leighton, 1988), whereas sexual maturity was stimulated with white or red, but not blue, light (Scott and Payne, 1937). Schonberg (U.S. Pat. No. 4,625,728) discloses that green light (400 to 600 nm) increases the growth rate of very young chickens, including embryos, while near red light (600 to 670 nm) induces maximal sexual development and may improve egg production. However, Jones et al. (1982) found that red light during the prebreeder or breeder periods was not beneficial for egg production.
Siopes (1984a) found no differences in egg production, fertility, or poult weight when hens were exposed to incandescent (IN) or full-spectrum fluorescent (FL) light treatments or when exposed to cool-white or full-spectrum FL light treatments, respectively (Siopes, 1984b). Felts et al. (1990) reported significantly higher hen-day egg production only during the first 10 weeks of the production period for females exposed to sodium vapor (SV) or daylight FL (DF) lights than for those under IN lights. On the other hand, Hulet et al. (1992) found no significant differences in egg production when hens were exposed to SV, DF, or IN lights.
Light intensity is also considered an important characteristic that relates to egg production. In a study comparing filtered-red light with white light at 85 and 160 1×, Jones et al. (1982) found that at 85 1×, egg production was equal between the two light sources. However, at 160 1×, hens exposed to white light had decreased egg production over those hens exposed to 84 1×. Pyrzak and Siopes (1986b; 1986c; 1989) examined the effects of equalized (photons/cm2/second) blue, green, and red light on egg quality and oviposition behavior. The authors found no difference in oviposition rate or patterns, but found that red light caused hens to lay heavier eggs with great quantities of albumen per egg. Pyrzak et al. (1987) report that eggs laid under blue or green light were consistently larger then those laid under red light (Pyrzak et al., 1987).
Siopes (1991) reported that light intensity from IN light ranging from 54 to 324 1× had no significant effect on reproductive performance of caged turkey hens. Pyrzak and Siopes (1986a) relate that reproductive performance was not different among turkey hens exposed to either IN, blue, green, or red light when the intensity (photons/cm2) remained constant. Felts et al. (1992) disclose that in the presence of a male, female breeder turkeys exposed to a fixed intensity with a DF light source (peak 495–590 nm, green to yellow) or to a SV light source (peak 580 nm, yellow) produced significantly more eggs than those under an IC light source (570 to 700 nm, yellow to red). Rozenboim et al. (1998) exposed prelaying pullets to one of three light treatments: 0.1 or 0.01 W/m2 with LED lamps (560 nm, 660 nm or 880 nm) and 0.1 W/m2 mini-fluorescent lamps. They report that a significant reduction in egg production was found in the 880 nm group and that no differences in egg production were found in other groups.
The reproductive efficiency of turkeys is generally low. Thus, turkeys are one example of poultry where the need to enhance reproductive performance is particularly high. One component of this low efficiency is the small amount of egg laying, which is related to a variable propensity toward cessation of egg laying and associated incubation behavior (broodiness). The term “broodiness” describes the behavior and physiological state associated with the maternal care of unhatched eggs. The expression of broody behavior by turkey hens is a costly problem to turkey breeders and producers of hatching eggs, resulting in a substantial loss of egg production.
Thus, what is needed is a method to enhance the reproductive performance of poultry, e.g., egg production in turkeys.